Authenticating identification and security documents and other objects

ABSTRACT

This patent document discloses physical documents including metameric ink pairs. One claim recites a document comprising: a first surface; a second surface, in which the first surface comprises a first set of print structures and a second set of print structures, in which the first set of print structures and the second set of print structures collective convey an encoded signal discernable from optical scan data representing at least a first portion of the first surface, in which the first set of print structures is provided on the first surface with a first ink and the second set of print structures is provided on the first surface with a second, different ink, and in which the first ink and the second, different ink comprise a metameric pair. Of course, other claims and combinations are described as well.

RELATED APPLICATION DATA

This application is a continuation of U.S. application Ser. No.15/650,447, filed Jul. 14, 2017 (U.S. Pat. No. 10,543,711) which is acontinuation of U.S. application Ser. No. 14/805,122, filed Jul. 21,2015 (U.S. Pat. No. 9,718,296), which is a continuation of applicationSer. No. 13/488,942, filed Jun. 5, 2012 (U.S. Pat. No. 9,087,376) whichis a continuation of U.S. application Ser. No. 12/970,629, filed Dec.16, 2010 (U.S. Pat. No. 8,194,919), which is a continuation of U.S.application Ser. No. 11/270,802, filed Nov. 8, 2005 (U.S. Pat. No.7,856,116) which claims the benefit of U.S. Provisional PatentApplication Nos.: 60/626,529, filed Nov. 9, 2004; 60/651,814, filed Feb.10, 2005; 60/670,773, filed Apr. 11, 2005; and 60/674,793, filed Apr.25, 2005. This application is related to assignee's U.S. Pat. No.6,754,377 (including Appendix A); U.S. Pat. Nos. 5,850,481; 5,636,292;5,710,834; 5,748,763; 5,748,783; 5,841,978; 5,832,119; 5,822,436(including the entire certificate of correction); U.S. Pat. Nos.5,862,260; 6,122,403; 6,026,193; 5,809,160; and publication Nos. US2004-0250080 A1 and US 2005-0041835 A1. Each of these patent documentsis hereby incorporated by reference in its entirety.

BACKGROUND AND SUMMARY

The present disclosure relates to steganography, digital watermarkingand security enhancements.

Digital watermarking is a form of steganography that encompasses a greatvariety of techniques by which plural bits of digital data are hidden insome other object without leaving human-apparent evidence of alteration.

Digital watermarking may be used to modify media content to embed amessage or machine-readable code into the content. The content may bemodified such that the embedded code is imperceptible or nearlyimperceptible to the user, yet may be detected through an automateddetection process.

Most commonly, digital watermarking is applied to media such as images,audio signals, and video signals. However, it may also be applied toother types of data, including documents (e.g., through line, word orcharacter shifting, through texturing, graphics, or backgrounds, etc.),software, multi-dimensional graphics models, and surface textures ofobjects.

Digital watermarking systems typically have two primary components: anembedding component that embeds the watermark in the media content, anda reading component that detects and reads the embedded watermark. Theembedding component embeds a watermark by altering data samples of themedia content (e.g., pixel values, DCT coefficients, waveletcoefficients, etc). The reading component analyzes content to detectwhether a watermark is present. In applications where the watermarkencodes information, the reading component extracts this informationfrom the detected watermark. Commonly assigned U.S. Pat. Nos. 6,614,914and 5,862,260 discloses various encoding and decoding techniques.

Some aspects of the disclosure relate to inconspicuously embeddingbinary data in line art images (such as are used in currency, graphics,identification documents and the like), and associated methods/systemsfor decoding such data from such images. Other aspects of the disclosurerelate to security features and confidence clues for identificationdocuments, currency, graphics and the like. Still other aspects of thedisclosure provide related systems and methods.

In the following disclosure it should be understood that references towatermarking encompass not only the assignee's watermarking technology,but can likewise be practiced with any other watermarking technology.

Some of the prior art in image watermarking has focused on pixelatedimagery (e.g. bit-mapped images, JPEG/MPEG imagery, VGA/SVGA displaydevices, etc.). In some watermarking techniques, the luminance or colorvalues of component pixels are slightly changed to effect subliminalencoding of binary data through the image. (This encoding can be donedirectly in the pixel domain, or in another domain, such as the DCTdomain.) In some systems, isolated pixels are changed in accordance withone or more bits of the binary data; in others, plural domain-relatedgroupings of pixels (e.g. locally adjoining, or corresponding to a givenDCT component) are so changed. In all cases, however, pixels have servedas the ultimate carriers of the embedded data.

One inventive technique for authentication and copy detection employsink pairs to provide authentication clues for security documents (e.g.,banknotes, currency, checks, financial instruments, etc.) andidentification documents (e.g., driver's license, passport, visa, IDcard, bank cards, etc.). An ink pair cooperates to provide a diffractiongrating (or other reflective pattern) while obscuring the location of ametallic ink—one of two inks in an ink pair.

According to one aspect, a document includes a first surface and asecond surface. The first surface comprises a first set of printstructures and a second set of print structures. The first set of printstructures and the second set of print structures cooperate to obscurethe location on the first surface of the second set of print structures.The second set of print structures is arranged on the first surface soas to provide a reflective pattern.

In a related example, the reflective pattern forms a diffractiongrating.

In another related example, the first set of print structures isprovided on the first surface with a first ink and the second set ofprint structures is provided on the first surface with a seconddifferent ink. The second different ink is a metallic ink.

In still another related example, the first set of print structures andthe second set of print structures collective convey a steganographicsignal (e.g., a digital watermark) that is discernable from optical scandata representing at least a first portion of the first surface.

According to another aspect of the disclosure, a photo identificationdocument includes a first surface and a second surface. The secondsurface includes a photographic representation (e.g., a picture orphoto) of an authorized bearer of the photo identification document. Thefirst surface comprises a first set of print structures provided thereonwith a first ink having a first color and a second set of printstructures provided thereon with a second ink having a second color. Thefirst color and the second color are visually similar colors. The firstset of print structures and the second set of print structures cooperateto obscure the location on the first surface of the second set of printstructures. The second ink comprises metallic characteristics so whenarranged on the first surface, the second set of print structuresprovide a diffraction grating.

According to still another aspect of the disclosure, a security document(e.g., a banknote, check, note, draft, etc.) includes a first surface; afirst set of print structures provided on the first surface with a firstink having a first color; and a second set of print structures providedon the first surface with a second ink having a second color. The firstcolor and the second color are visually similar colors. The first set ofprint structures and the second set of print structures cooperate toobscure the location on the first surface of the second set of printstructures. The second ink comprises metallic characteristics so whenarranged on the first surface, the second set of print structuresprovide a pattern that, in response to a signal or radiation, reflects apredetermined signal or pattern.

The foregoing features and advantages of the disclosure will be morereadily apparent from the following detailed description, which proceedswith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show prior art techniques for achieving grayscaleeffects using line art.

FIG. 2 shows a virtual array of grid points that can be imposed on animage according to one embodiment of the present disclosure.

FIG. 3 shows a virtual array of regions that can be imposed on an imageaccording to the FIG. 2 embodiment.

FIG. 4 shows an excerpt of FIG. 3 with a line from a line art imagepassing therethrough.

FIG. 5 shows changes to the width of the line of FIG. 3 to effectwatermark encoding according to one embodiment of the presentdisclosure.

FIG. 6 shows changes to the position of the line of FIG. 3 to effectwatermark encoding according to another embodiment of the presentdisclosure.

FIG. 7 is a block diagram of a photocopier according to anotherembodiment of the disclosure.

FIG. 8 shows a line angle modulation watermark signal.

FIG. 9 a shows a first surface of a document including a transparent orsemi-transparent window; and FIG. 9 b shows of a second surface of thedocument including the transparent or semi-transparent window.

FIG. 10 shows a relationship between cash and confidence.

FIG. 11 illustrates a document including a first surface.

FIG. 11A illustrates an ink pair arranged in a pattern on the firstsurface of FIG. 11 . This area is enlarged for the reader's convenience.

FIGS. 11B and 11C illustrate ink pairs arranged in alternative patterns.

FIG. 11D illustrates ink dots or blobs arranged to provide a reflectivepattern. The dots or blobs are enlarged for the reader's convenience.

FIG. 12 illustrates the appearance of the FIG. 11A pattern to a casualhuman observer.

FIG. 13 highlights a portion of a diffraction grating for the FIG. 11Apattern.

FIG. 14 illustrates pattern detection for a transceiver/authenticator.

FIG. 15 illustrates an exaggerated view of a security document includingsecurity fibers.

FIG. 16 illustrates a spatial mapping of the fibers shown in FIG. 15 .

FIG. 17 illustrates a portable consumer device displaying the spatialmapping of FIG. 16 .

FIG. 18 is a diagram illustrating observation of a watermarked image atan off-normal viewing angle.

DETAILED DESCRIPTION

Line Art

While pixelated imagery is a relatively recent development, line artgoes back centuries. One familiar example is U.S. paper currency. On theone dollar banknote, for example, line art is used in several differentways. One is to form intricate webbing patterns around the margin of thenote (generally comprised of light lines on dark background). Another isso form grayscale imagery, such as the portrait of George Washington(generally comprised of dark lines on a light background).

There are two basic ways to simulate grayscales in line art. One is tochange the relative spacings of the lines to effect a lightening ordarkening of an image region. FIG. 1A shows such an arrangement; area Blooks darker than area A due to the closer spacings of the componentlines. The other technique is to change the widths of the componentlines—wider lines resulting in darker areas and narrower lines resultingin lighter areas. FIG. 1B shows such an arrangement. Again, area B looksdarker than area A, this time due to the greater widths of the componentlines. These techniques are often used together.

Some specific embodiments of steganographic encoding using line arttechniques are provided below.

One embodiment posits a virtual grid of points imposed on a line artimage (e.g. a U.S. one dollar banknote), with the points spaced atregular intervals in vertical and horizontal directions. (The horizontaland vertical intervals need not be equal.) The virtual points may beimposed over some or all of the bill at equal vertical and horizontalspacings of 250 μm. In regions of the banknote having line art, thecomponent lines of the art snake in and amongst these virtual gridpoints.

Each grid point is considered to be the center of a rounded-squareregion. The luminance of the region is a function of the proximity ofany line(s) within the boundary of the region to the region'scenterpoint, and the thickness of the line(s).

To change the luminance of the region, the contour of the line(s) ischanged slightly within the region. In particular, the line is madeslightly thicker to decrease luminance; or thinner to increase luminance(Unless otherwise noted, dark lines on light backgrounds are presumed.)The ability to effect these slight changes is then employed, inaccordance with known pixelation-based watermarking techniques, toencode binary data in the line art. If such a banknote is thereafterscanned by a scanner, the values of the pixel data produced by thescanner will reflect the foregoing alterations in luminance values,permitting embedded watermark data to be decoded.

In an alternative embodiment, the line widths are not changed. Instead,the positions of the lines are shifted slightly towards or away fromcertain virtual grid points to effect an increase or decrease in thecorresponding area's luminosity, with the same effect. Other embodimentsare also detailed.

By the techniques disclosed herein, line art images can be encoded tosubliminally convey binary data. This capability permits varioushardware systems to recognize banknotes, and to change or limit theiractions in a predetermined manner (e.g. a photocopier equipped with thiscapability can refuse to reproduce banknotes, or can insert forensictracer data in the copy).

Advances in digital imaging and printing technologies have vastlyimproved desktop publishing, yet have provided counterfeiters with lowcost technologies for illegally counterfeiting security documents (e.g.,banknotes, checks, notes, drafts, and other financial instruments) andidentification documents (e.g., driver's licenses, passports, IDdocuments, visa, etc.). While there are many technologies that makecounterfeiting more difficult, there is a need for technologies that canquickly and accurately detect originals and distinguish copies.Preferably, these technologies integrate with existing processes forhandling such documents.

Referring to FIG. 2 , an illustrative form of the disclosure employs agrid 10 of imaginary reference points arrayed over a line art image. Thespacing between points is 250 μm in the illustrated arrangement, butgreater or lesser spacings can of course be used.

Associated with each grid point is a surrounding region 12, shown inFIG. 3 . As described below, the luminosity (or reflectance) of each ofthese regions 12 is slightly changed to effect the subliminal encodingof binary data.

Region 12 can take various shapes; the illustrated rounded-rectangularshape is representative only. (The illustrated shape has the advantageof encompassing a fairly large area while introducing fewer visualartifacts than, e.g., square regions.) In other embodiments, squares,rectangles, circles, ellipses, etc., can alternatively be employed.

FIG. 4 is a magnified view of an excerpt of FIG. 3 , showing a line 14passing through the grid of points. The width of the line, of course,depends on the particular image of which it is a part. The illustratedline is about 25 μm in width; greater or lesser widths can naturally beused.

In a first embodiment of the disclosure, shown in FIG. 5 , the width ofthe line is controllably varied so as to change the luminosity of theregions through which it passes. To increase the luminosity (orreflectance), the line is made narrower (i.e. less ink in the region).To decrease the luminosity, the line is made wider (i.e. more ink).

Whether the luminance in a given region should be increased or decreaseddepends on the particular watermarking algorithm used. Any algorithm canbe used, by changing the luminosity of regions 12 as the algorithm wouldotherwise change the luminance or colors of pixels in a pixelated image.

In an exemplary algorithm, the binary data is represented as a sequenceof −1s and 1s, instead of 0s and 1s. (The binary data can comprise asingle datum, but more typically comprises several. In an illustrativeembodiment, the data comprises 100 bits.)

Each element of the binary data sequence is then multiplied by acorresponding element of a pseudo-random number sequence, comprised of−1s and 1s, to yield an intermediate data signal. Each element of thisintermediate data signal is mapped to a corresponding sub-part of theimage, such as a region 12. The image in (and optionally around) thisregion is analyzed to determine its relative capability to concealembedded data, and a corresponding scale factor is produced. Exemplaryscale factors may range from 0 to 3. The scale factor for the region isthen multiplied by the element of the intermediate data signal mapped tothe region in order to yield a “tweak” value for the region. In theillustrated case, the resulting tweaks can range from −3 to 3. Theluminosity of the region is then adjusted in accordance with the tweakvalue. A tweak value of −3 may correspond to a −5% change in luminosity;−2 may correspond to −2% change; −1 may correspond to −1% change; 0 maycorrespond to no change; 1 may correspond to +1% change; 2 maycorrespond to +2% change, and 3 may correspond to +5% change. (Thisexample follows the basic techniques described in the Real Time Encoderembodiment disclosed in U.S. Pat. No. 5,710,834.)

In FIG. 5 , the watermarking algorithm determined that the luminance ofregion A should be reduced by a certain percentage, while the luminanceof regions C and D should be increased by certain percentages.

In region A, the luminance is reduced by increasing the line width. Inregion D, the luminance is increased by reducing the line width;similarly in region C (but to a lesser extent).

No line passes through region B, so there is no opportunity to changethe region's luminance. This is not fatal to the method, however, sincethe watermarking algorithm redundantly encodes each bit of data insub-parts spaced throughout the line art image.

The changes to line widths in regions A and D of FIG. 5 are exaggeratedfor purposes of illustration. While the illustrated variance ispossible, most implementations will modulate the line width 3-50%(increase or decrease).

(Many watermarking algorithms routinely operate within a signal marginof about +/−1% changes in luminosity to effect encoding. That is, the“noise” added by the encoding amounts to just 1% or so of the underlyingsignal. Lines typically don't occupy the full area of a region, so a 10%change to line width may only effect a 1% change to region luminosity,etc. Banknotes are different from photographs in that the art need notconvey photorealism. Thus, banknotes can be encoded with higher energythan is used in watermarking photographs, provided the result is stillaesthetically satisfactory. To illustrate, localized luminance changeson the order of 10% are possible in banknotes, while such a level ofwatermark energy in photographs would generally be consideredunacceptable. In some contexts, localized luminance changes of 20, 30,50 or even 100% are acceptable.)

In the illustrated embodiment, the change to line width is a functionsolely of the tweak to be applied to a single region. Thus, if a linepasses through any part of a region to which a tweak of 2% is to beapplied, the line width in that region is changed to effect the 2%luminance difference. In variant embodiments, the change in line widthis a function of the line's position in the region. In particular, thechange in line width is a function of the distance between the region'scenter grid point and the line's closest approach to that point. If theline passes through the grid point, the full 2% change is effected. Atsuccessively greater distances, successively less change is applied. Themanner in which the magnitude of the tweak changes as a function of lineposition within the region can be determined by applying one of variousinterpolation algorithms, such as the bi-linear, bi-cubic, cubicsplines, custom curve, etc.

In other variant embodiments, the change in line width in a given regionis a weighted function of the tweaks for adjoining or surroundingregions. Thus, the line width in one region may be increased ordecreased in accordance with a tweak value corresponding to one or moreadjoining regions.

Combinations of the foregoing embodiments can also be employed.

In the foregoing embodiments, it is sometimes necessary to trade-off thetweak values of adjoining regions. For example, a line may pass along aborder between regions, or pass through the point equidistant from fourgrid points (“equidistant zones”). In such cases, the line may besubject to conflicting tweak values—one region may want to increase theline width, while another may want to decrease the line width. (Or bothmay want to increase the line width, but differing amounts.) Similarlyin cases where the line does not pass through an equidistant zone, butthe change in line width is a function of a neighborhood of regionswhose tweaks are of different values. Again, known interpolationfunctions can be employed to determine the weight to be given the tweakfrom each region in determining what change is to be made to the linewidth in any given region.

In the exemplary watermarking algorithm, the average change inluminosity across the image is zero, so no generalized lightening ordarkening of the image is apparent. The localized changes in luminosityare so minute in magnitude, and localized in position, that they areessentially invisible (e.g. inconspicuous/subliminal) to human viewers.

An alternative embodiment is shown in FIG. 6 , in which line position ischanged rather than line width.

In FIG. 6 the original position of the line is shown in dashed form, andthe changed position of the line is shown in solid form. To decrease aregion's luminosity, the line is moved slightly closer to the center ofthe grid point; to increase a region's luminosity, the line is movedslightly away. Thus, in region A, the line is moved towards the centergrid point, while in region D it is moved away.

It will be noted that the line on the left edge of region A does notreturn to its nominal (dashed) position as it exits the region. This isbecause the region to the left of region A also is to have decreasedluminosity. Where possible, it is generally preferable not to return aline to its nominal position, but instead permit shifted lines to remainshifted as they enter adjoining regions. So doing permits a greater netline movement within a region, increasing the embedded signal level.

Again, the line shifts in FIG. 6 are somewhat exaggerated. More typicalline shifts are on the order of 3-50 μm.

One way to think of the FIG. 6 embodiment is to employ a magnetismanalogy. The grid point in the center of each region can be thought ofas a magnet. It either attracts or repels lines. A tweak value of −3,for example, may correspond to a strong-valued attraction force; a tweakvalue of +2 may correspond to a middle-valued repulsion force, etc. InFIG. 6 , the grid point in region A exhibits an attraction force (i.e. anegative tweak value), and the grid point in region D exhibits arepulsion force (e.g. a positive tweak value).

The magnetic analogy is useful because the magnetic effect exerted on aline depends on the distance between the line and the grid point. Thus,a line passing near a grid point is shifted more in position than a linenear the periphery of the region.

Each of the variants discussed above in connection with FIG. 5 islikewise applicable to FIG. 6 .

Combinations of the embodiments of FIGS. 5 and 6 can of course be used,resulting in increased watermark energy, better signal-to-noise ratioand, in many cases, less noticeable changes.

In still a further embodiment, the luminance in each region is changedwhile leaving the line unchanged. This can be effected by sprinklingtiny dots of ink in the otherwise-vacant parts of the region. In highquality printing, of the type used with banknotes, droplets on the orderof 3 μm in diameter can be deposited. (Still larger droplets are stillbeyond the perception threshold for most viewers.) Speckling a regionwith such droplets (either in a regular array, or random, or accordingto a desired profile such as Gaussian), can readily effect a 1% or sochange in luminosity. (Usually dark droplets are added to a region,effecting a decrease in luminosity. Increases in luminosity can beeffected by speckling with a light colored ink, or by forming lightvoids in line art otherwise present in a region.)

In a variant of the speckling technique, very thin mesh lines can beinserted in the artwork—again to slightly change the luminance of one ormore regions.

Although not previously mentioned, it is contemplated that the banknotewill include some manner of calibration information to facilitateregistration of the image for decoding. This calibration information canbe steganographic or overt. Several techniques for steganographicallyembedding calibration information are disclosed in my prior patents andapplications. Other techniques can be found in others of the cited work.

To decode watermark data, the encoded line art image must be convertedinto electronic form for analysis. This conversion is typicallyperformed by a scanner.

Scanners are well known, so a detailed description is not provided here.Suffice it to say that scanners conventionally employ a line of closelyspaced photodetector cells that produce signals related to the amount ofthe light reflected from successive swaths of the image. Mostinexpensive consumer scanners have a resolution of 300 dots per inch(dpi), or a center to center spacing of component photodetectors ofabout 84 μm. Higher quality scanners of the sort found in mostprofessional imaging equipment and photocopiers have resolutions of 600dpi (42 μm), 1200 dpi (21 μm), or better.

Taking the example of a 300 dpi scanner (84 μm photodetector spacing),each 250 μm region 12 on the banknote will correspond to about a 3×3array of photodetector samples. Naturally, only in rare instances will agiven region be physically registered with the scanner so that ninephotodetector samples capture the luminance in that region, and nothingelse. More commonly, the line art is skewed with respect to the scannerphotodetectors, or is longitudinally misaligned (i.e. somephotodetectors image sub-parts of two adjoining regions). However, sincethe scanner oversamples the regions, the luminance of each region canunambiguously be determined.

In one embodiment, the scanned data from the line art is collected in atwo dimensional array and processed—according to one of the techniquesdisclosed in my prior patents and applications—to detect the embeddedcalibration information. The array is then processed to effect a virtualre-registration of the image data. A software program then analyzes thestatistics of the re-registered data (using the techniques disclosed inmy prior writings) to extract the bits of the embedded data.

In a variant embodiment, the scanned data is not assembled in a completearray prior to the processing. Instead, it is processed in real-time, asit is generated, in order to detect embedded watermark data withoutdelay. (Depending on the parameters of the scanner, it may be necessaryto scan a half-inch or so of the line art image before the statistics ofthe resulting data unambiguously indicate the presence of a watermark.)

In accordance with another aspect of the disclosure, various hardwaredevices are provided with the capability to recognize embedded watermarkdata in any line art images they process, and to respond accordingly.

One example is a color photocopier. Such devices employ a color scannerto generate sampled (pixel) data corresponding to an input media (e.g. adollar bill). If watermark data associated with a banknote is detected,the photocopier can take one or more steps.

One option is simply to interrupt copying, and display a messagereminding the operator that it is illegal to reproduce currency.

Another option is to dial a remote service and report the attemptedreproduction of a banknote. Photocopiers with dial-out capabilities areknown in the art (e.g. U.S. Pat. No. 5,305,199) and are readily adaptedto this purpose. The remote service can be an independent service, orcan be a government agency.

Yet another option is to permit the copying, but to insert forensictracer data in the resultant copy. This tracer data can take variousforms. Steganographically encoded binary data is one example. An exampleis shown in U.S. Pat. No. 5,568,268. The tracer data can memorialize theserial number of the machine that made the copy and/or the date and timethe copy was made. To address privacy concerns, such tracer data is notnormally inserted in photocopied output, but is so inserted only whenthe subject being photocopied is detected as being a banknote. (Such anarrangement is shown in FIG. 7 .)

Desirably, the scan data is analyzed on a line-by-line basis in order toidentify illicit photocopying with a minimum of delay. If a banknote isscanned, one or more lines of scanner output data may be provided to thephotocopier's reprographic unit before the banknote detection decisionhas been made. In this case the photocopy will have two regions: a firstregion that is not tracer-marked, and a second, subsequent region inwhich the tracer data has been inserted.

Photocopiers with other means to detect not-to-be-copied documents areknown in the art, and employ various response strategies. Examples aredetailed in U.S. Pat. Nos. 5,583,614, 4,723,149, 5,633,952, 5,640,467,and 5,424,807.

Another hardware device that can employ the foregoing principles is astandalone scanner. A programmed processor (or dedicated hardware)inside the scanner analyzes the data being generated by the device, andresponds accordingly.

Yet another hardware device that can employ the foregoing principles isa printer. A processor inside the device analyzes graphical image datato be printed, looking for watermarks associated with banknotes.

For both the scanner and printer devices, response strategies caninclude disabling operation, or inserting tracer information. (Suchdevices typically do not have dial-out capabilities.)

Again, it is desirable to process the scanner or printer data as itbecomes available, so as to detect any banknote processing with aminimum of delay. Again, there will be some lag time before a detectiondecision is made. Accordingly, the scanner or printer output will becomprised of two parts, one without the tracer data, and another withthe tracer data.

We sometimes refer to the above techniques as “Line Width Modulation” or“LWM.” And, as mentioned above, other techniques for embeddinginformation may include spots and holes for floods and blank areas anddirected holes.

Another technique, as disclosed in assignee's U.S. patent applicationSer. No. 10/723,181 (published as US 2004-0263911 A1) is referred to as“Line Continuity Modulation or “LCM”. This method embeds watermarks bymodulating a continuity of line structures. For example, an auxiliarysignal is embedded in a line image by selectively breaking the lineswhere the embedding location value is zero. Another example encodeswatermark information by introducing subtle modifications in a designstructures to create light and dark areas corresponding to watermarkcomponents or data carriers.

LWM and LCM can be thought of as part of a broad class of techniquesthat encode a digital watermark by modulating characteristics of adesign structure to create subtle light and dark areas corresponding tobinary 1s and 0s.

Additional inventive techniques and combinations are described below.

Line Angle Modulation—

Line structures often have a dominant angle or orientation. One way ofembedding watermark information is to vary (modulate) the line angleswithin the design to create 0s and 1s. For example, the vertical linesrepresent 0s and the horizontal lines represent is (or a distancebetween horizontal lines represents data.) In another implementation atransition between a first angle (e.g., a horizontal) and a second angle(e.g., a vertical) conveys data. In still another implementation, linesor graphics can be oriented with respect to a know angle of structureprovided on a document. For example, a visible fiducial or graphicprovides a base orientation through its own orientation. Then,orientation of line structures around the document are evaluated todetermine their orientation with respect to the visible fiducially orgraphic. These techniques can be used to embed robust watermarks. Thismethod embeds a watermark using Line Angle Modulation such that thewatermark is preferably not visible in the original, e.g., the linestructures appear as a uniform field in the original document. Aftercopying, due to limitations of the copying process, certain anglesalias, and cause the watermark to appear in the copy. An example of sucha watermark is shown in FIG. 8 . A watermark

Line Frequency Modulation—

A digital watermark can also be embedded by modulating the frequency ofthe line structures. This technique provides additional flexibility intying the watermark feature closely with the design structures. Forexample, for line structures having constant width (thickness), thefrequency of the structures can be increased or decreased to embed 1sand 0s. The frequency is used to convey the data.

An alternative method of using frequency modulation “warps” or contortsan image to carry the watermark information. Consider that a design islaid out on a stretchable surface. Now imagine compressing the designstructures in some areas and stretching the design structures in otherareas to create dense and sparse regions respectively. Compressedregions will appear darker (more ink in given area) while stretchedregions appear lighter (less ink in given area). This process can beused to encode watermark information.

Line Thickness Modulation—

This technique is a modification of the LWM technique. Here, the widthof each line structure, or of a set of line structures, is maintainedconstant throughout its length. However, the width of adjacent linestructures are varied to embed 0s and 1s. In contrast with LWM, thistechnique may apply to sparser design structures.

Combination of Techniques—

Multiple techniques can be combined in the design elements throughoutthe design depending upon the characteristics of the design structures.These techniques can be used to embed multiple watermarks at differentresolutions as well. For example, LCM can be used for higher resolutionwatermarks whereas Line Frequency Modulation and Line ThicknessModulation are favorable for encoding lower resolution watermarks.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these and other combinations asclaims in this or continuing applications.

A1. A method of watermarking an image to convey auxiliary data, whereinthe image including a plurality of line elements, the method comprises:

determining a base line width;

varying a frequency of at least a set of line element relative to thebase line width to convey a plural-bit message.

A2. A method of watermarking an image to convey auxiliary data, whereinthe image including a plurality of elements, the method comprises:

receiving the image;

selectively contorting the image to provide relatively dense and sparseregions of elements, wherein the dense and sparse regions convey aplural-bit message.

A3. The method of A2, wherein said contorting comprises at least one ofresizing, scaling, stretching and warping.

A4. A method comprising:

determining a base orientation for media from a graphic or visiblefiducial;

determining an orientation for a plurality of line structures relativeto the base orientation, and

deciphering a plural-bit code based on the foregoing.

Document Authentication

Cell phones continue to proliferate throughout the world's population.Many of today's cell phones and personal digital assistants (PDAs) aresophisticated computing devices, including optical sensors (e.g., CCD orCMOS sensors) for image and video capture. These optical sensorstypically provide a color (or monochrome) output. A few examples includeNEC's 525 phone, Fujitsu's F900 phone and Nokia's 3620 phone. Of course,these examples are provided by way of example only. Many of these phonesand PDAs include robust processing and memory capability, allowing forsophisticated signal processing (e.g., digital watermark decoding andpattern recognition). In the case of color images or video, the colorchannels include, e.g., Red, Green and Blue. The image or video istypically displayed to a user of the device via a display. A population,armed with these types of mobile computing devices, have newauthentication techniques available to them.

In the past, identification documents and banknotes (sometimes referredto hereafter as “currency”) have included several lines of defensive (orauthenticating) security features. First line-security features, thosethat are distinguishable by casual inspection, include optical variabledevices (OVD), including holograms, kinegrams, optical variable ink,visible or analog watermarks, and intaglio inks. Second line-securityfeatures are generally more covert, like digital watermarks.

The proliferation of mobile computing devices allows us to blur theselines of defenses.

Consider an identification document that includes a plurality of colors(e.g., via ink or dye) provided on a first surface. One of the colors isyellow. We provide a visual graphic in the yellow channel, e.g., like animage of an eagle or snake. The yellow graphic is hard—but notimpossible—to see with an unaided human eye. The visual graphic mightalso be further obscured by adjusting an overall luminance in an area inwhich the graphic is printed by offsetting or lowering the color valuesof other colors (e.g., black) in that area. Related techniques aredisclosed in assignee's U.S. Published Patent Application No. US2002-0164052 A1 and in PCT Application No. PCT/US02/20832 (published inEnglish as WO 03/005291). Each of these patent documents is herebyincorporated by reference.

A consumer—armed with an imaging mobile device—captures optical scandata representing the identification document. As mentioned above, themobile device includes an optical sensor that provides a plurality ofcolors (e.g., RGB). The mobile device selects the blue channel fordisplay (or at least emphasizes the blue channel) to the consumer.(Imaging software, e.g., products by Adobe provided tools to allowseparation of color channels. Other software provides similar tools.Indeed, display drivers can be programmed to selectively display aparticular color channel like a blue color channel.) The yellow channelgraphic is pronounced in the blue channel display, since the yellowcolor graphic results in more light being absorbed, which is readilydetectable in the blue channel. The consumer views the graphic on hermobile display to ascertain an authentication clue. For example, themere presence of the graphic provides some confidence that theidentification document is authentic.

A related approach can be used with ultraviolet or infrared inks, if themobile optical sensor is fitted (e.g., IR or UV filtering) toaccommodate such.

Printing alignment continues to be a cornerstone in the secure printingworld. Precise or aligned printing can be used to provide preciselylocated features, fine-lined graphics, etc. Precise front to backalignment also provides authentication clues.

An improvement is to combine aligned printing with digital watermarking.In a first implementation, a visual feature is provided on a surface ofan identification document. The visual feature might be obscured, asdiscussed above with the yellow channel graphic. The identificationdocument includes steganographic encoding, perhaps in the form ofdigital watermarking. The encoding includes plural-bit data. The datacarries or links to registration information associated or cooperatingwith the visual feature. In a first example, the registrationinformation includes information to reproduce a related feature. In thisexample, the first feature includes a first geometric pattern (like acircle). The registration information includes spatial coordinates anddimensions for a second feature. The second feature preferably includesa second geometric pattern (like a matching circle).

A mobile device captures optical scan data representing the encodedidentification document. Software (or dedicated circuitry) executing ona mobile device decodes the steganographic encoding from the capturedoptical scan data to obtain the registration information. Software usesthe registration information to generate (e.g., graphically displayedrelative to the image of the first feature) the second geometric patternand align it for display on the mobile device. In some cases the firstand second patterns are intended to overlap or intertwine in an expectedmanner Misalignment or mis-registration relative to the first featureindicates a potential counterfeit.

(Unless extreme care is taken with the printing of the first feature—andcorresponding alignment of the second feature—the expected alignment ofthe first and second features may be spatially mis-registered. We notehere that alignment and registration of the second feature may be easedwith pattern recognition software. For example, the pattern recognitionsoftware identifies the first feature based on its shape (or pattern). Aplacement location of the second feature can be based on a location ofthe first feature, once found. Edge detection software can also be usedto determine a location of the first feature. An edge of the document orfeature can be used to identify a location. If a counterfeiter makes thefirst feature too small, or offsets the first feature, the rendering ofthe second feature will not correspond as expected. Of course, we canuse a registration component carried by steganographic encoding toresize, translate or rotate the captured imagery if needed.)

In some cases, the first feature is laid down on a substrate using afirst printing plate (and color), while the steganographic encoding islaid down on the substrate using a second printing plate (and color). Inthe first example discussed above, registration or alignment between thetwo printing plates provides additional security, since alignment isrequired in order to properly generate a second feature relative to thefirst feature.

Another example uses printing alignment of a front surface and a backsurface. Consider the document in FIGS. 9 a and 9 b . FIG. 9 a shows afirst surface (e.g., front surface) of an identification document. Thedocument includes a first window. The window may include a transparentor semi-transparent polymer or may include a pressed area (e.g., pressedpaper) to provide some transparency, perhaps aided by a light source.The first surface window may include a graphic, image, texturing orbackground printing. The graphic, image, texturing or backgroundprinting includes first steganographic encoding.

FIG. 9 b shows a second surface (e.g., back surface) of theidentification document. The window is seen on the second surface aswell. The second surface window may include a graphic, image, texturingor background printing. The graphic, image, texturing or backgroundprinting includes second steganographic encoding.

The first and second steganographic encodings cooperate to provide anauthentication clue.

For example, a mobile device captures an image of the window from eithera viewpoint of the first or second surface. Since the window istransparent or semi-transparent, both the first and secondsteganographic encoding is optically captured with a single-sided scanof the window. The spatial relation of the first and secondsteganographic encoding can be used to determine whether the documentwas properly registered when originally printed. Mis-registrationsignals a potential counterfeit document.

The first and second steganographic encoding can cooperate in other waysas well. For example, the first steganographic encoding may include aplural-bit payload that indicates a relative and expected spatiallocation of the second steganographic encoding.

The scale, rotation and/or translation of the first and secondsteganographic encoding, relative to each other, is another indicationof original printing misalignment (a telltale sign of a counterfeiteddocument). Watermark orientation parameters are even further discussed,e.g., in assignee's U.S. Pat. Nos. 6,614,914, 6,704,869 and 6,385,329,which are each hereby incorporated by reference.

Of course, plural-bit payloads, each carried by the first and secondsteganographic encoding can be redundant or cross-correlated forauthentication.

Digital watermarking can also be used to provide anonymity for currencysubstitutes. We envision users to one-day print cash substitutes athome, at mall kiosks or on the road.

Digital watermarks are used in these situations to provide relatedinformation. A digital watermark may include a message or payload thatis used to indicate a “one-use” only requirement. The message, oncedecoded, is used to interrogate a data structure which keeps track ofwhether the cash substitute has ever been used before. The watermark mayalso include a “good-until” indicator, issuing authority, amount, etc.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these and other combinations asclaims in this or continuing applications.

B1. An identification document or banknote comprising:

a substrate including a first surface and a second surface;

a transparent or semi-transparent window disposed in the substrate,wherein the window is viewable from both the first surface and thesecond surface,

first steganographic encoding on the first surface window side; and

second steganographic encoding on the second surface window side.

B2. The document or banknote of B1, wherein the first steganographicencoding and the second steganographic encoding cooperate to yieldauthentication clues.

B3. The document or banknote of B2, wherein the cooperation provides arelative spatial alignment of the first steganographic encoding and thesecond steganographic encoding.

B4. The document or banknote of B3, wherein the relative spatialalignment of the first steganographic encoding and the secondsteganographic encoding comprises at least one of rotation, scale andtranslation.

B5. The document or banknote of any one of B1-B4, wherein the firststeganographic encoding comprises a first plural-bit message and thesecond steganographic encoding comprises a second plural-bit message,and wherein the cooperation comprises a redundancy or cross-correlationof the first and second messages.

B6. The document or banknote of any one of B1-B4, wherein the firststeganographic encoding and the second steganographic encoding are bothdetectable from a single optical scan of either the first surface orsecond surface.

B7. The document or banknote of any one of B1-B6, wherein the substratecomprises a first material and the window comprises a second, differentmaterial.

B8. The document or banknote of B7, wherein the first material comprisespaper or a paper synthetic.

B9. The document or banknote of B7 or B8, wherein the second materialcomprises a plastic or polymer.

C1. A banknote or identification document comprising:

a substrate;

multi-color printing on the substrate, wherein the multi-color printingincludes a first feature printed therein in a yellow color, wherein theyellow color first feature is obscured to an unaided human eye.

C2. A method of analyzing the banknote or identification document of C1with a handheld computing device, wherein the handheld computing devicecomprises at least an optical sensor, electronic processing circuitryand a display, said method comprising:

receiving optical scan data of the banknote or identification documentfrom the optical sensor;

providing blue channel color information for display on the display,wherein the first feature is readily perceptible on the display to anunaided human eye.

C3. The method of C2, wherein the device comprises a cell phone orpersonal digital assistant.

C4. The method of any one of C2 and C3, wherein the banknote oridentification document comprises steganographic indicia encodedtherein.

C5. The method of C4, wherein the steganographic indicia comprisesregistration data.

C6. The method of C5, wherein the registration data comprises or linksto a second feature.

C7. The method of C6, wherein the device comprises instructions forexecution on the electronic processing circuitry to: i) recognize thefirst feature; ii) generate for display on the display the secondfeature at an alignment relative to the first feature.

C8. The method of any one of C1-C7 wherein only blue channel colorinformation is provided for display on the display.

C9. The method of any one of C1-C7 wherein the blue channel colorinformation is emphasized relative to other color information whendisplayed.

Metallic Inks

Specialized, metallic inks have emerged which allow electronic circuitry(e.g., RFIDs) to be “printed” on document substrates.

Some examples of electronic circuitry are shown, e.g., in assignee'sU.S. Pat. No. 6,608,911 and published U.S. Patent Application No. US2003-0178495 A1 (allowed). Each of these documents is hereinincorporated by reference.

One improvement embeds a digital watermark in a circuit layout itself.Subtle changes to line widths or ink contrast are employed in thecircuit layout when it is printed, laid down, etched, or fabricated. Forexample, the line modulation techniques disclosed herein may be used toencode a watermark signal in a circuit layout. The subtle changes conveya digital watermark, which is detectable through optical scan data ofthe circuit. Even a circuit diagram can include the watermark embeddedtherein. Imagine a product label or product packaging that is printedwith an RFID metallic ink layer. The layer is optically scanned and thewatermark is discerned there from.

Identification documents and banknotes may include electronic circuitry.The circuitry may be passive, in that it requires an external energy orfrequency source to excite the circuitry. The circuitry may beresponsive at any desired frequency (e.g., even extending into the highGigahertz range). The circuitry may include a variety of elements likeminiature light emitting diodes and piezoelectronic or audio devices.

When excited by an appropriate stimulus (e.g., exposure to a particularenergy or transmission frequency) the electronic circuitry is energized.In a first example, the identification document or banknote “shines” viathe LED. The shinning provides an authentication clue. In a secondexample, the identification document or banknote vibrates via aminiature piezoelectronic transducer upon exposure to an appropriatestimulus. In a third example, the identification document or banknoteemits an audible sound via a miniature piezo-audio device upon exposureto an appropriate stimulus. In a fourth example, a digital watermarkcarried by the identification document or banknote includes a key orseed value. The key or seed value, once decoded from the digitalwatermark, is used to tune the external stimulus to a particularfrequency or setting. Once tuned, the stimulus excites or energizes theelectronic circuitry.

In a related implementation, an identification document or banknoteincludes passive (or active) electronic circuitry. The electroniccircuitry emits (perhaps only after external stimulation) a firstfrequency. A reader emits a second frequency, and employs a heterodyningprocess to generate a third frequency based on the first and secondfrequencies. The third frequency is used to determine authenticity ofthe document or banknote. In some implementations, the first frequencyemitted by the electronic circuitry is used as a key or seed, which isused to select an appropriate second frequency for the heterodyningprocess.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these combinations as claims inthis or continuing applications.

D1. A banknote comprising:

a substrate;

printing on the substrate; and

electronic circuitry carried on or in the substrate, wherein theelectronic circuitry is passive and activates in response to apredetermined energy or frequency.

D2. The banknote of D1, wherein the electronic circuitry includes apiezo-electronic device.

D3. The banknote of D2, wherein the piezo-electronic device vibrateswhen the electronic circuitry is activated in response to thepredetermined energy or frequency, the vibration providing a sensoryauthentication clue.

D4. The banknote of D2, wherein the piezo-electronic device emits anaudible sound when the electronic circuitry is activated in response tothe predetermined energy or frequency, the sound providing an audibleauthentication clue.

D5. The banknote of D1, wherein the electronic circuitry comprises alight emitting element which is activated in response to thepredetermined energy or frequency, the activated light emitting elementcomprising a visual authentication clue.

D6. A reader cooperating with the banknote of any one of D1-D5,comprising:

an energy or frequency source;

a receiver to receive a first frequency emitted by the electroniccircuitry;

a determination module to determine whether a frequency corresponds toan expected frequency, and if so, to provide a signal indicating suchdetermination.

D7. The reader of D6, wherein the energy or frequency source excites theelectronic circuitry.

D8. The reader of D6, wherein the energy or frequency source emits asecond frequency, and wherein the determination module heterodynes thefirst and second frequencies to yield a third frequency, wherein thethird frequency compared for correspondence to the expected frequency.

D9. A method comprising:

providing an electronic circuit on a surface through metallic ink,wherein the electronic circuit yields a plural-bit identifier whenexcited, and wherein the electronic circuit is provide so that anoptical scan of the electronic circuit will yield a steganographicsignal.

D10. The method of D9, wherein the steganographic signal is providedthrough subtle changes to lines of the electronic circuit.

D11. The method of D1l wherein the steganographic signal compriseplural-bit data.

D12. The method of any one of D9-D11 wherein the plural-bit identifierand the plural-bit signal coincide.

D13. The method of any one of D9-D12 wherein the electronic circuitcomprises an RFID.

Now with reference to FIG. 10 , we detail a relationship between cashand consumer confidence. We refer to this figure as a “dumbbell” model.One the left side, cash (or money) is represented both in the physicalworld (e.g., paper banknotes and checks, etc.) and electronic or cyberworld (e.g., digital cash and financial records/credit). The left sideof the dumbbell is balanced by confidence and brand protection on theright side. In order for the cash to have any meaningful significance, aconsuming base must believe or have confidence in the physical orelectronic manifestation of the currency. An example is currency brand.Historically the US currency has been a strong “brand” of currency.

Digital watermarks are used to support the FIG. 10 model. For example, adigital watermark is used to bridge the gap between physical andelectronic cash. A unique identifier is associated with an account or“credit”. The watermark or unique identifier is associated with theelectronic cash, and is conveyed when the credit is converted to aphysical form. The watermark is used for authentication, as discussedabove.

Security through Metameric Ink Pairs

Inks and Dyes

A first embodiment of this aspect of the present disclosure employs apair of similarly colored inks or dyes. For example, these inks may betermed so-called “metameric” inks.

Metameric inks work on a principle of metamerism; that is, two colorsmatching or approximating one another under one set of conditions canappear or behave quite differently under another set of conditions.

We preferably employ a pair of metameric inks that appear (visually)about the same under normal or visible lighting conditions. The term“about” in this application takes on its typical meaning of“approximately,” “similar” or “close to,” etc.

The inks differ, however, in that one ink in the ink pair is a metallicink. The metallic ink includes metal pigments, platelets or otherportions that provide the ink with metallic characteristics (e.g.,radiation reflectance).

Arrangement on a Surface

We arrange a pair of metameric inks on a first surface 12 (FIG. 11 ) ofan identification or security document 10 to achieve at least twogoals: 1) visual obfuscation of a metal ink; and ii) creation of adiffraction grating on the first surface via the metallic ink. Our useof the terms “diffraction grating” envisions a grating or pattern thatcan at least “reflect” or “diffract” energy or radiation. (We sometimesrefer to a diffraction grating or pattern as a “metal grating,”“reflection pattern” or “reflection grating.”)

FIG. 11A illustrates a portion of the first surface 12. An ink pair isprovided in a pattern. As illustrated, the pattern includes a line artimage (e.g., such as are sometimes used in security documents, graphics,identification documents and the like). Of course, our techniques arenot limited to line art images and can be employed in many othergraphics, images and patterns as well.

The ink pair, Blue (B) and Metallic Blue (MB), is arranged as shown inFIG. 11A. The Blue ink (B) and the Metallic Blue ink (MB) are arrangedto form continuous lines on a surface. The lines appear continuous andabout the same color (or at least very similar in color) to a casualhuman observer of the surface (FIG. 12 ). This similar appearanceresults since the Blue (B) ink and Metallic Blue (MB) ink are ametameric pair. A casual human observer is preferably not aware of thelocation of the metal ink—meeting goal no. 1 above. (We note that manyink and dye manufactures, e.g., including Pantone, Inc., with a NorthAmerican office in Carlstadt, N.J. USA, provide matching metallic andnon-metallic inks.)

The Blue (B) and Metallic Blue (MB) inks transition at position 20 asshown in FIG. 11A. Since some metallic inks have a “shine” or “luster,”human observation of the transition 20 can be lessened by providing thinlines. In other embodiments, we provide lines or shapes in a dotmatrix-like fashion. In those embodiments, we can overprint the Blue (B)ink into the Metallic Blue (MB) regions to lessen a stark transition.

The inks can be arranged in accordance with, e.g., known printingprocesses. In a preferred implementation, however, we employ a printingprocess including at least two printing plates. A first plate prints theBlue (B) ink and a second plate prints the Metallic Blue (MB) ink. Tightplate registration is preferred to achieve visually continuous patternsas shown in FIG. 11A. (We note that high end printing presses, likethose used for printing security documents like currency, provideexceptional plate registration capabilities.) Of course other printingtechniques can be used so long as sufficient printing registration ofthe non-metallic ink and the metallic ink is maintained.

With reference to FIG. 13 , a Metallic Blue (MB) ink is provided toyield a reflection pattern (or diffraction grating). That is, theMetallic Blue (MB) ink includes reflective properties that, whenarranged in a pattern on first surface 12, provide a diffraction gratingcapable of reflecting or diffracting high frequency radiation orillumination. A portion of the grating is shown with bolded MetallicBlue (MB) sections in FIG. 13 . The illustration deemphasizes (shownwith dashes) the non-metallic Blue (B) ink since Blue (B) ink lacks anysignificant contribution to the metal grating. The diffraction gratingis designed to yield a desired frequency response (or reflectionpattern) when illuminated with an energy or radiation source.

Some care is preferably taken when designing a diffraction grating.

In a first situation, where a designer has somewhat unfettered designdiscretion, a diffraction pattern is laid out (perhaps computer-assistedto achieve a particular reflection pattern, as is common nowadays), andthen an obfuscation pattern is formed around the diffraction grating.For example, Metallic Blue (MB) ink is mapped to the diffraction gratingdesign, and then Blue (B) ink is provided in concert with the MetallicBlue (MB) ink to form a visual design that helps conceal the location ofthe Metallic Blue (MB) ink.

In a second, perhaps more common situation, a host or carrier image isprovided. For an identification document, the host image may include,e.g., a state seal or graphic, and for a security document, the hostimage may include, e.g., a bank logo, line-art or background pattern.Using the host image as a template, a diffraction grating is designed toblend within the host image—sometimes this process is referred to asgenerating an “interference” or “composite” image. The interference orcomposite image represents both the host image and the diffractiongrating. If the host image includes line art, line segments areidentified to host metallic ink that will form a diffraction grating. Ifthe host image includes an image or graphic, regions within the imageare identified to receive grating portions.

A shading or tinting effect might be added to a host image, where theshading or tinting comprises a plurality of parallel or smoothly curvinglines provided with metallic ink. Such shading hosts the diffractiongrating. A host image can also be filled in or created with “dots” or“blobs” where a set of the dots or blobs include fine lines or areasprovided with metallic ink (FIG. 11D). The set of dots or blobscollectively provide a diffraction grating. Non-metallic ink dots orblobs can be intertwined with their metallic cousins to obfuscate thelocation of the metal dots—and consequently the location and design ofthe diffraction grating. (More generally, metallic dots can be laid downto provide a diffraction grating on a surface of a security oridentification document.)

Regardless of the technique used, identified areas of a diffractiongrating are used to guide metallic ink placement.

Line spacing for a diffraction grating is preferably determined withconsideration of the illumination source (e.g., 60-75 GHz), so that thegrating can accommodate the radiation or illumination wavelengths andprovide a desired reflection beam or pattern response. We prefer thatour lines be on the order of about a millimeter or less, but otherdimensions can be used according to a given design criteria. Distancebetween lines or dots can be adjusted to accommodate a desiredreflection response, as is known to those of ordinary skill in the art.

In some implementations we use a pseudo-randomly generated spatialpattern to help identify locations for placing metallic ink. Oncelocations are identified, metallic ink is laid down to provide areflectance pattern. A key (perhaps assigned to an issuing authority)can be used to seed a pseudo-random pattern generator.

Still other examples of arranging ink pairs are shown in FIGS. 11B and11C. FIG. 11B shows parallel lines, resulting in a somewhat typicaldiffraction grating formation. The straight lines contrast to thecurvilinear grating shown in FIG. 11A. FIG. 11C illustrates MetallicBlue (MB) ink that is over-printed or printed adjacent to selectedsegments of Blue (B) ink. This technique lays down a thin line or shadowat selected areas. This technique can be advantageously used toobfuscate locations of the Metallic Blue (MB) ink as well.

Of course there are still many other arrangements that can be made tovisually obscure a metal ink while providing a diffraction grating. Wenote that some implementations will have a transition area between firstand second inks. This transition area allows for a gradual changebetween first ink and the second ink, which will help if inks noticeablydiffer in color or sheen.

Excitation or Energy Source

An excitation source excites the diffraction grating, e.g., excites theMetallic Blue (MB) ink, as seen in FIG. 14 . An excitation source (e.g.,transceiver 40) preferably illuminates in the range of 50-80 Gigahertz,but most preferably in the range of 60-75 Gigahertz. The source can beaccommodated in a handheld device (e.g., a keychain FOB, adapted cellphone, or the like) or mounted at a stationary location (e.g., point ofsale location).

In a first implementation the excitation source 40 emits a burst (orchirp) at a predetermined frequency (e.g., 72 Gigahertz). Thediffraction grating or pattern (metallic ink) reflects the energy in apattern in accordance with its design.

In a second implementation the energy sources emits a chirp or burstthat cycles through a range of frequencies (e.g., ramps up from 60 GHzto 75 GHz, and then perhaps back down to 60 GHz again). The chirp signalreflects from the diffraction grating or pattern in accordance with thegrating's pattern.

Illumination and resulting reflectance is shown, albeit in a simplifiedmanner, in FIG. 14 . Transmitted radiation (or energy) is shown withsolid lines and reflected radiation is shown in returning hashed lines.

The excitation source includes a receiver, perhaps even a MIMO (multipleinputs, multiple outputs) or SIMO (single input, multiple outputs)receiver, which includes multiple transmitters and receptors.

An authenticator module 45 (FIG. 14 ) determines a signature fromreflected radiation patterns (e.g., reflection or beam patterns or aplurality of “peaks” representing reflection angles or phaserelationships, etc.) over the cycled frequency range or a reflectionpattern corresponding to a single reflection. The signature need notinclude all features from a reflected pattern, but instead may includeone or more attributes of a received reflectance pattern. If usingmultiple transmitters and/or receivers, a signature may contemplatereceived interference patterns as well. The authenticator module 45determines whether the signature matches (or coincides within apredetermined tolerance) an expected signature.

Different organizations (e.g., different states when issuing driver'slicenses) can each be assigned a unique signature (and correspondinggrating pattern). Different types of documents can be similarlydistinguished (e.g., a first signature for a passport, and a seconddifferent signature for a visa, or a first signature for a firstdenomination of currency and a second different signature for a seconddenomination of currency).

The authenticator module 45 may cycle through a list of expectedpatterns to determine whether a received pattern matches at least one ofthe expected patterns. The identification document or security documentis authenticated when a signature matches (or coincides within apredetermined tolerance) an expected pattern or signal. The document isconsidered suspect absent such a match.

Combined with Watermarking

In some cases we prefer a subtle color or contrast variance between thefirst ink and the metallic ink. The color or contrast variance is slightso as to be generally unnoticeable by a casual human observer. Themetallic and non-metallic inks are arranged to provide both adiffraction grating and a digital watermark.

For example, Line Width Modulation techniques (LWM) or Line ContinuityModulation (LCM) techniques can be used to pattern a digital watermark(see, e.g., Published Application No. US 2005-0041835 A1 and U.S. Pat.No. 6,449,377).

The digital watermark pattern can be considered when designing adiffraction grating. (Redundant encoding and error correction encodingcan help ensure that both a watermark signal and a diffraction gratingare sufficiently produced.) Thus, an identification document includesboth a watermark (observable from scan data) and a diffraction grating(verified through received radiation patterns) conveyed through the samepair of inks.

Organic Light Emitting Diodes

Organic polymers and other materials have recently led to the commercialviability of so-called “organic light emitting diodes” or “OLED” display(or “array” or “matrix”). OLEDs and methods of manufacturing such arefurther discussed, e.g., in U.S. Pat. Nos. 6,664,564, 6,670,052,6,774,392 and 6,794,676, which are each hereby incorporated byreference.

An improvement is to provide an OLED display on an identificationdocument or banknote.

One can imagine the possibilities. An OLED display can provided aluminous pattern, perhaps to show an expected currency denomination(e.g., text or number) or identification document type, or a graphic orseal. The displayed graphic or seal may include a hidden signal, e.g., adigital watermark embedded therein. An optical scan of the OLED willinclude the hidden signal embedded in the graphic or seal.

With the aid of micro-circuitry, the luminous pattern can change. Thatis, the pattern can alternate between different patterns, or betweentext and patterns, etc.

The OLED display is provided on or in a first area of the document orbanknote. In some implementations, but certainly not required, the firstarea is a see-through, thin plastic window. The OLED display can beactivated with an on-document power supply, e.g., a micro battery. Inother implementations, the document or banknote includes piezoelectricdevice(s). Friction or movement of the document or banknote activatesthe piezoelectric devices, which creates a current to activate the OLEDdisplay. In still other implementations, the OLED display includes orcooperates with passive circuitry; that is, circuitry that generates orresponds to an electric field. The current is provided to the OLEDdisplay for activation. In still other implementations, a document orbanknote includes a contact, and power is transferred to the document orbanknote through the contact. Another possible power source is solarenergy or other light source.

Related to the above discussion, in other implementations polymer thinfilm electronics are provided to create a layer of plastic with an arrayof transistors and LEDs across the surface of a film. The film layer isintegrated within a document structure (e g, laminate onto core layer,for example). The circuitry can be driven with a power supply, e.g., anon-document supply, such as a battery, or a contact or interface thatreceives power from an external power source. In either case the powerenergizes the LED array. The LED array can be used to displayinformation, e.g., including information stored in the document(biometric information, demographic information, etc.). This is easy toimagine when the document includes electronic memory circuitry, e.g.,such as is provided by a so-called smart card. Information from thememory circuitry is communicated to the LED array for display. But evenpaper thin documents, e.g., banknotes, can carry information. A seriesof transistors (e.g., organic TFT) are provided on the document, or in alayer of the document. The transistors form a memory cell, which caninclude information like a serial number, denomination, or hash ofinformation printed on the document.

Information carried by the document or banknote can interact withexternal information supplied to the document through an interface.Consider a document that includes a wireless interface. The documentreceives information through the interface. In some implementations theinformation is a key (e.g., of a key pair) that decrypts informationencrypted on the card with the other key of the pair (e.g., aprivate/public key pair). The decrypted information is displayed via theLED array. If the information is legible or expected the document isconsidered authentic, otherwise the document is considered suspect.

Of course, this technology has application in a wide variety of securedocuments, including bank cards, financial instruments, bank notes,cards and documents, etc.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these and other combinations asclaims in this or continuing applications.

E1. A financial instrument or identification document comprising:

a substrate;

a power supply carried on or in the substrate;

electronic circuitry carried on or in the substrate; and

an organic light emitting diode (OLED) display carried on or in thesubstrate and powered by the power supply and controlled or driven, atleast in part, by the electronic circuitry.

E2. The financial instrument or identification document of E1, whereinthe power supply comprises at least one of a battery, a passive-currentgenerating device, solar or light conversion cell, and a piezoelectricdevice.

E3. The financial instrument or identification document of E1, whereinthe electronic circuitry comprises memory with first information storedtherein.

E4. The financial instrument or identification document of E3, whereinat least some of the first information is communicated to the OLEDdisplay via the electric circuitry for display thereon.

E5. The financial instrument or identification document of E4, whereinthe at least some of the first information that is communicated to theOLED display comprises at least one of a currency denomination, agraphic, seal, text, and number.

E6. The financial instrument or identification document of E4 whereinthe at least some of the first information that is communicated to theOLED display comprises first display information and second displayinformation, wherein the electronic circuitry provides timing of thefirst display information and the second display information so that thefirst display information is first displayed by the OLED display andthen the second display information is displayed by the OLED display.

E7. The financial instrument or identification document of any one ofE1-E6 wherein the instrument comprises at least one of a banknote,currency, check, note, draft, traveler's check, security interest, bondand certificate.

E8. An identification document comprising:

a substrate;

a power supply carried on or in the substrate;

electronic circuitry carried on or in the substrate; and

a light emitting diode (LED) matrix carried on or in the substrate andpowered by the power supply and controlled or driven, at least in part,by the electronic circuitry.

E9. The identification document of E8 wherein the electronic circuitrycomprises polymer-based thin film electronics.

E10. The identification document of E8 wherein the electronic circuitryand LED matrix are carried by a thin film layer carried by thesubstrate.

E11. The identification document of E10 wherein the thin film layer islaminated to the substrate.

E12. The financial instrument or identification document of E3, whereinthe first information comprises an encrypted form.

E13. The financial instrument or identification document of E12, whereinthe document or instrument further comprises an interface to receivesecond information.

E14. The financial instrument or identification document of E13, whereinthe second information comprises a key to decrypt the first informationprior to display on the LED display.

E15. The financial instrument or identification document of E3 whereinthe substrate comprises at least one of printing, engraving and aphotograph, and the first information comprises information thatcorresponds to or is redundant with the printing, engraving andphotograph.

E16. The financial instrument or identification document of E15 whereinthe substrate comprises multiple, separate layers.

E17. The financial instrument or identification document of any one ofE1-E7 and E12-E16, wherein the instrument or document comprises at leastone of a banknote, currency, check, note, draft, traveler's check,security interest, bond and certificate, driver's license, passport,visa and national id.

Interference of Thin Films

A phenomenon of light interference in thin films (e.g., think of soapywater) is well understood and has been leveraged to create a broad arrayof security features since copying or altering objects with these typesof “light interference” features is difficult.

Constructive and destructive interference of light due to internalreflection at a boundary of the thin film creates a desired effect ofshifting spectral reflection as a function of several differentparameters, most notably an “angle of incidence.”

A simple example of this effect is shifting of spectral reflection ofsoapy water from a center point of 536 nm to 455 nm when the angle ofincidence moves from normal to 45 degrees.

This property of shifting spectral reflection can be used to create adigital watermark that can only be observed by viewing a watermarkedimage at an angle off normal (see FIG. 18 ). The modulation in spectralresponse (e.g., the watermark itself) is created by varying a thicknessof the film, which can be accomplished by any number of techniquesincluding screening of the image (assuming it is being printed withpearlescent ink that displays these properties) or the film itself canbe produced to vary in thickness.

To recover the watermark, the document is illuminated with white lightand viewed at the specified angle. The recover process can be augmentedby using an equivalent of, e.g., a notch-filter or with illumination ofa specific wavelength (e.g., truncating higher spectral frequencies,with reference to the dashed line in FIG. 18 ).

The techniques centered on a single film can be easily extended tomultiple films that are stacked to create much larger shifts in spectralresponse.

In another embodiment, this increase in spectral shifts, combined withmore complex behaviors, can be used to impart a number of differentbehaviors on a watermark itself. For example:

-   -   Increased Fragility: Frequency band where a watermark appears is        tightly controlled, such that only with very narrow-band        illumination or with a notch filter can the watermark be read.    -   Tamper Evidence: By imparting fragility in the structure itself        (e.g., varying the adhesives between films) a watermark is        designed such that a component of the watermark is carried in        the fragile film, such that if the document is tampered with and        the film was separated, the watermark would no longer read. A        variant of this is having a watermark appear if tampering        occurs. This can be abstracted to create a system wherein        integrity of a thin-film based security feature can validated in        an automated fashion, layer by layer.    -   Interdependence: Similar to physical security, a watermark can        only be read by knowing the “recipe” of where and how to        illuminate a structure to recover the watermark. This recipe may        include multiple observation points, illumination sources and        filtering. All requiring that all the observed spectral shifts        are co-located such that the watermark is still readable (e.g.,        think of plate-registration, but taken to three dimensions. Each        layer must be registered (X,Y) and the thickness has to be        correct (Z)).    -   Appearance of disappearance of wave-bands: In another        embodiment, a perceived double to single waveband shift (e.g.,        both spectral responses shift, but one might shift into UV,        hence making it non-visible) is used to weaken or allow a        watermark to appear.        Retroreflection

Retroreflection as phenomena has been leverage from securityapplications (e.g., 3M's Confirm laminate) for safety clothing (e.g., areflective vest for running at night). The angle of reflection andspectral response can now be controlled through various manufacturingprocesses.

Through the modulation of both of these parameters (i.e., angle ofreflection and spectral response, as well as other parameters) awatermark can be encoded in retroreflective material. Similar to theprior embodiment using thin films, the watermark appears, disappears orchanges (including yielding a different payload at different observationangles) as a function of the observed angle.

WORM Watermark

Prior to the mass availability of CD Burners and acceptance of such intothe common vernacular (to “burn” something means the permanent writingof) this functionality was referred to as Write Once Read Many (i.e.,“WORM”). Many embodiments of this existed, where only portions of thedisk were writeable, etc.

A digital watermark equivalent is one that allows its payload (e.g.,plural-bit message) to be encoded and embedded and then altered in thefield after a watermarked image is produced on a substrate.

For example:

-   -   Encode watermark template in a substrate, but add/modify message        to the substrate after production by using techniques such as is        used in DCards, where the substrate itself is heated locally and        causes a “browning” of the PVC substrate where heated.    -   Destroy specific “cells” within retro-reflective laminate to        locally change the spectral response when viewed at a specific        angle.

For statistics-based encoding or decoding, remarking “resets” thestatistics of the image, so that the image can be re-marked. Remarkingdoes have visual impacts though, so only a limited number of overwritesare currently possible.

Physical Random Functions in Security Printing

Advances in digital imaging and printing technologies have vastlyimproved desktop publishing, yet have provided counterfeiters with lowcost technologies for illegally counterfeiting security documents (e.g.,banknotes, checks, notes, drafts, and other financial instruments) andidentification documents (e.g., driver's licenses, passports, IDdocuments, visa, etc.). While there are many technologies that makecounterfeiting more difficult, there is a need for technologies that canquickly and accurately detect originals and distinguish copies.Preferably, these technologies integrate with existing processes forhandling such documents.

By way of some additional background, and with reference to thesemiconductor world, we often find naturally occurring variances incircuit manufacturing. For example, doping levels of productionmaterials (e.g., semi-conductors) slightly vary from device to device.These slight variations have been leveraged to create addressable logic,and are sometimes referred to as “Physical Random Functions” (or “PRFs”or “PUFs”).

This addressable logic (or, more generally, the device's uniquevariations) are used to uniquely identify a specific circuit, used as aseed for a random number generator and even used as a key for acryptographic process. One advantage of Physical Random Functions isthat they are based on what is believed to be fundamentally randomprocess that is hard to control or predict; hence, the random featuresare hard to counterfeit.

Many printing process have a number of PRFs as well. The variations orfunctions have been used in forensic analysis of documents and toidentify types of printers. See, e.g., Mikkilineni, et al., “Printeridentification based on graylevel co-occurrence features for securityand forensic applications,” in Security, Steganography, and Watermarkingof Multimedia Contents VII, edited by Edward J. Delp III, Ping Wah Wong,Proceedings of the SPIE-IS&T Electronic Imaging, SPIE Vol. 5681, pages430-440 (2005), which is herein incorporated by reference. Suchvariations or functions might include plate registration, ink density,dot gain, printer characteristics, and other printing characteristics.For inkjet or toner based systems, variations or distinctive patterns inink/toner spray, banding artifacts or drop-outs can be identified.

We extend the use of PRF features to create a machine-readable (or atleast a machine-observable) feature that can be read in an automatedfashion for printed security and identification documents.

One implementation relies on a random placement of so-called securityfibers during security document manufacture. Security paper fibers aresometimes mixed in with raw paper pulp during paper manufacture. Sometimes the paper pulp is a cotton and linen concoction. (Foridentification documents, fibers or fluorescent particles can be mixedin a document substrate or layer during, e.g., a molding process.) Somecurrencies leverage color fibers (some of which are UV sensitive) intheir paper making process, see, e.g., the Crane & Co. paper. Due to theintroduction of the fibers in the paper pulp, the fibers are lodged inthe substrate as opposed to being on the surface. The fiber's placementwithin the substrate protects them from undue soiling and wear. Anexaggerated example of such fibers in a document is shown in FIG. 15 .These fibers find themselves arranged in a security document in a randommanner—akin to Physical Random Functions seen in semiconductor devices.

The random arrangement of such fibers allows for a calculation of aunique signature or fingerprint based on the fibers. Such features canbe observed with an optical imager (e.g., optical scanner or cell phonecamera) or some other instrument typically used in the field (e.g.,magnetic head for magnetic characteristics, IR or UV camera forout-of-visible spectrum characteristics, etc.). The signature orfingerprint can include a representation of a spatial relationship ofall fibers or a set of fibers. This representation, once determined, canbe used to seed a number generator or hashing algorithm. The resultingnumber is the unique identifier. Or a slope of one or more of thesecurity fibers can be calculated and used as an identifier; related isa calculation of a second derivative for one or more of the fiber'sshape (or slope curvature). The result is used as an identifier or as aseed to a number generator or hashing algorithm. Of course otheridentifying techniques based on the security fibers can be used as well.

The result of such calculations is an identifier that uniquelyrepresents a security document based on the PRF nature of the securityfibers.

Applications of PRF's

One application using PRFs is tracking and monitoring. Documents aremonitored as they flow through distribution centers. An optical scannerscans each document (or a sampling of such documents) as the documentsflow by. The optical scan data is analyzed by a monitor (e.g., softwareor hardware monitor) to calculate unique identifiers for the respectivedocuments.

One can imagine a counterfeiting scenario that includes copying onedocument and reproducing it time and time again. (The fibers arerepresented with color ink in the copies. Each copy will then have thesame PRF characteristic as its parent document.) If a monitor recognizesthe same or statistically similar identifiers time and time again, themonitor can issue an alert for an emerging counterfeiting threat.

PRF's Combined with Other Machine Readable Features

As discussed above, a PRF can be used to create a unique identifier fora document (e.g., a 256-bit identifier). A unique identifier can be usedin cooperation with digital watermarking and other machine-readableindicia.

For example, a digital watermark embedded in a document may carry anumber resulting from PRF analysis.

(Behind the scenes, a PRF is read from an unprinted document substrate,e.g., via optical scanning of the substrate. Resulting optical scan datais analyzed and a unique identifier based on the PRFs is generated therefrom. The unique identifier is provided to an embedder. The embedderembeds the unique identifier as, e.g., a digital watermark or overt 2-Dsymbology. The watermarking or symbology is provided on the documentduring printing.)

In another, related embodiment, a document is modified each time it isinspected and validated. For example, a document is modified in somemachine-recognizable fashion each time the document passes through acentralized facility. A document can be subtly reprinted to includeanother machine-readable component (e.g., a digital watermarkcomponent). Perhaps the component is only one or two bits (e.g.,introduced through changing luminance characteristics of the document atpredetermined areas, or relative to other digital watermark components).But the bit change indicates an inspection and successful validation.The document is subsequently modified each time it is inspected anddeemed valid. (A validity determination is made based on a successfulcalculation and verification of the PUF. For example, the PUF is checkedagainst a “watch list” of suspected identifiers, or can be compared to amachine-readable version of the same). Instead of modifying the documentthrough printing, other techniques like exposure to predetermined lightor radiation may be used. In these later cases, the document includes,e.g., photosensitive materials that change with exposure to the light orradiation.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these and other combinations asclaims in this or continuing applications.

F1. A method of monitoring for counterfeited documents comprising:

optically scanning a plurality of documents;

identifying a physically random function associated with each of theplurality of documents;

determining if the physically random function associated with each ofthe plurality of documents are statistically similar; and

signaling such a similarity when it arises.

F2. The method of F1 wherein the physically random function isdetermined from fibers found in the documents.

F3. A method comprising:

determining a physically random function (PRF) associated with adocument;

representing the PRF as a plural-bit identifier; and

steganographically embedding the plural-bit identifier in artwork orgraphics carried by the document.

F4. The method of F3 wherein the graphics comprise at least a photographof an authorized bearer of the document.

Advances in First-Line Defenses

Historically, “first-line” inspection has referred to inspectiontechniques that are carried out through visual inspection and/or touch.First-line inspection has been a cornerstone of security printing sinceits inception.

Technology proliferation has forced reevaluation of first-lineinspection techniques, both from a threat and benefit side.Counterfeiting technology has advanced to a point where any first-linetechniques are now easily counterfeited. At the same time high-qualityimagers with significant resolution (300 DPI+) are being widelydistributed (e.g., on cell phone cameras).

A series of first-line “+” approaches are needed. We outline a few “+”approaches below. Some of these approaches modify existing features thatare inspected with aid of widely available consumer devices. Otherapproaches introduce new features and functionality. Examples ofavailable consumer devices include, e.g., cell phones, PDAs (e.g., thinkPocket PCs) and portable music players, each that include an opticalimager (or camera) and a display. These devices are augmented to includesoftware to facilitate the functionality noted below. Instead ofsoftware, hardware implementations are acceptable as well. (Artisans ofordinary skill will be able to make and use such software without undueexperimentation given this disclosure relative to what is already knownin the art.)

In a first implementation a document includes extraordinarily smallmicro-print that is imperceptible to the naked human eye. A user (e.g.,at a point of sale location) optically scans a document with hercamera-equipped cell phone. Software executing on the cell phoneanalyzes the optical scan data, finds and then magnifies themicro-printing, and presents the magnified micro-printing via a devicedisplay. The software may include a character recognition module thatallows recognition of the micro-printing. If an error is found in themicro-printing (or if an expected error is not found) the devicepreferably prompts the user of such. Preferably, only those documentregions including such micro-printing are provided via display for userinspection. (In some cases the ASCII values of micro-printing are hashedand compared against a predetermined or expected value. The user isnotified if the calculated and expected values differ significantly).

In some variations of this first implementation, the micro-printing isprovided on the document surface in proximity to a fiducial or hashmark. The fiducial provides a recognizable feature for the characterrecognition software. The fiducial's presence signals an expectedpresence of micro-printing. Once a region is identified as including thefiducial, a predetermined area around the fiducial is searched forexpected micro-printing. The micro-printing is presented to a user via adevice display.

In a second implementation, a document includes materials that fluorescein the near-IR spectrum (e.g., many available inks have near-IRresponses). While this fluorescence is beyond human perceptibly, many oftoday's devices (e.g., camera-equipped cell phones) are sensitive tothis portion of the spectrum. The camera picks up features conveyed inthe near-IR, which are presented to the user via the display. The use ofnear-IR in the art of security printing is well known. One variation ofthis second implementation includes a camera that picks up fluoresce orreflection from “hidden” features. These hidden features may be visiblesolely in the near-IR or may require an additional filter with aspecific spectral response to highlight the feature. Another variationof this implementation involves illuminating a document with a light orstrobe (a feature that is becoming common on cell phones & PDA's) thatenable the feature to become visible.

A third implementation harkens back to our above discussion of PRF's.Consider a document that includes security fibers or other visuallyperceptible features. A spatial mapping of the features is determined(see FIG. 16 ). The mapping is represented by an identifier or othercharacteristics. The identifier or characteristics are provided as amachine-readable component (e.g., as a digital watermark component orpayload).

The digital watermark may also include a so-called orientationcomponent, which is helpful in resolving image distortion such asrotation, scaling and translation. See, e.g., assignee's U.S. Pat. Nos.6,704,869, 6,408,082, 6,122,403 and 5,862,260, which are each herebyincorporated by reference. In some cases a spatial mapping of thefeatures is conveyed as a watermark orientation component, much like amapping of fingerprint minutia discussed in assignee's U.S. PublishedPatent Application No. US 2005-0063562 A1, published Mar. 24, 2005,which is hereby incorporated by reference.

A user scans a document with her camera (e.g., cell phone or PDA). Awatermark reader reads a watermark from the scan data to obtain theembedded identifier or characteristics. Cooperating softwarereconstructs an expected, relative spatial placement of the securityfibers based on the embedded identifier or characteristics. The expectedspatial placement is provided to the user via the device display. Thepresentation may include, e.g., a graphical representation of anexpected placement of security fibers relative to the document (see FIG.17 ). The representation can include dots, lines, marks, etc. In someimplementations, an image of the document is shown in the display (ascaptured by the device) and a graphical overlay is provided over thedocument to show the expected placement of the security fibers. A usercan visually check the document to determine accurate placement.

Another variation automatically determines an actual placement of PRFindicators (e.g., security fibers) and presents via a device display theactual placement vs. the expected placement. The actual placement of PRFindicators is found through, e.g., analysis of optical scan data.

Instead of placement of security fibers, a watermark may reveal anexpected location, shape or details of other document features such asdesigns, seals, etc.

A watermark payload may be secured through cryptographic means toprovide additional security. A public key is provided to a user's deviceto decode a watermark payload. The public key can be used to validate adigital signature issued by a document issuing authority for thedocument being inspected. The hash used to create the digital signaturewould be based on a PRF or PUF. The digital signature would be createdand embedded into a machine readable feature during printing.

A fourth implementation relies on so-called high-resolution watermarks(fragile, robust, tamper-evident, etc.). These watermarks may only bedetectable through high resolution scanning Resolutions of 10K DPI arecommon in security printing, this allows for machine readable featuresof the same resolution. By operating at this resolution, successfulattacks would be required to operate at a similar resolution if not 2×(Nyquist). This places the features well outside the range of currentimaging workflows (typically 1200-4800 DPI) and hence outside of all butthe most specialized of equipment usually reserved for security printers(e.g., Simultan Printing Presses, Jura RIPs, etc.). This frequency isalso in a similar band to where naturally occurring PRF's typicallyappear (ink bleed, dot gain, voids, etc.).

A fifth implementation relies on audible feedback. A tone is generatedby a device (e.g., cell phone, PDA, etc.) as an imager sweeps across adocument. The tone is triggered, e.g., when a watermark is detectedand/or when the watermark's payload matches or otherwise corresponds tothe predetermined PRF characteristics. In some variations of this fifthimplementation, an audible scale (e.g., think ring-tone) is influencedby the speed of the optical swipe. The ring tone will only sound or willvary in sound depending on the speed of the optical sweep (a simplegyroscope with speed measurement in the device can help facilitate thisfunctionality). Of course, speed of optical sweep and watermark/PRFdetection can be combined to generate a predetermined sound.

An important criteria in many of the above implementations is to leavethe decision process of whether a document is authentic to a humanobserver, and not to a device. For example, if authentication reliessolely on a device flashing a green light, signaling that a document isauthentic, counterfeiting attacks will target the device. Such attacksmight render device-determined authentication indications suspect.

Some possible combinations of this disclosure include the following. Ofcourse, other combinations will be evident to those of ordinary skill inthe art. We reserve the right to present these combinations as claims inthis or continuing applications.

G1. A method of authenticating a security or identification documentwith a handheld computing device, the device comprising an opticalsensor and a display, the document comprising micro-printing providedthereon, wherein the micro-printing is generally imperceptible by anunassisted human observer, said method comprising:

receiving from the optical sensor optical scan data corresponding to thedocument;

analyzing the optical scan data to recognize the micro-printing;

scaling or magnifying the micro-printing;

providing at least some of the scaled or magnified micro-printing viathe display.

G2. The method of G1 wherein the document further comprises amicro-printed fiducial.

G3. The method of G2 wherein the micro-printing is recognized at leastin part through identification of the fidicual.

G4. A handheld computing device comprising:

a display;

an optical sensor;

processing circuitry; and

electronic memory, wherein said memory comprises executable instructionsstored therein for execution by the processing circuitry, saidinstructions comprising instructions to carry out the method of any oneof F1-F3.

G5. A method of authenticating a security or identification documentwith a handheld computing device, the device comprising an opticalsensor, and at least a speaker, the document comprising machineobservable features provided thereon, said method comprising:

receiving from the optical sensor optical scan data corresponding to thedocument;

analyzing the optical scan data to observe the features;

based at least on observed features, providing an audible signal via thespeaker.

G6. The method of claim G5 wherein the audible signal is dependent on aspeed at which the optical sensor is moved for scanning relative to thedocument.

G7. The method of claim G5 wherein the machine observable featurescomprise digital watermarking.

G8. The method of claim G7 wherein the machine observable features arerandomly placed.

CONCLUDING REMARKS

Having described and illustrated the principles of the technology withreference to specific implementations, it will be recognized that thetechnology can be implemented in many other, different, forms. Toprovide a comprehensive disclosure without unduly lengthening thespecification, applicants hereby incorporate by reference each of thepatent documents referenced above.

The methods, processes, and systems described above may be implementedin hardware, software or a combination of hardware and software. Themethods and processes described above may be implemented in programsexecuted from a system's memory (a computer readable medium, such as anelectronic, optical or magnetic storage device).

We have used Blue (B) ink and Metallic Blue (MB) ink in some sections ofthe above discussion for consistency and to ease the description. Use ofthese inks are for illustration only should in no way limit thedisclosure. Indeed, we contemplate many different ink colors andfinishes. We also contemplate use of more than two types of ink, andmore than two printing plates. Also, reference to Pantone is forillustrative purposes also. There are many other suitable inkmanufacturers.

Of course, photocopying (color copying) a security document includingour metameric inks would be very difficult. First, the copy would needto include metallic ink capabilities. Further, even if a copying processincluded metallic ink, the metallic ink would need to be arranged sothat it was not readily distinguishable (e.g., visually distinguishable)from the non-metallic ink and would need to be arranged in a diffractionpattern to yield an expected signature.

The particular combinations of elements and features in theabove-detailed embodiments are exemplary only; the interchanging andsubstitution of these teachings with other teachings in this and theincorporated-by-reference patents/applications are also contemplated.

What is claimed is:
 1. A document comprising: a first surface; a secondsurface, in which the first surface comprises a first set of printstructures and a second set of print structures, in which the first setof print structures and the second set of print structures collectivelyconvey an encoded signal discernable from optical scan data representingat least a first portion of the first surface, and in which the secondset of print structures are arranged on the first surface so as toprovide a reflection pattern, in which the reflection pattern comprisesa diffraction grating, the diffraction grating provides a predeterminedreflection pattern yielding an energy signature upon excitation by aradio spectrum energy source, and in which the radio spectrum energysource emits in the range of 60-75 GHz.
 2. The document of claim 1 inwhich the second, different ink comprises a metallic ink.
 3. Thedocument of claim 1 in which the first set of print structures isprovided on the first surface with a first ink and the second set ofprint structures is provided on the first surface with a second,different ink, in which the second, different ink comprises a metallicink.
 4. The document of claim 3 comprising a security document or anidentification document.
 5. The document of claim 1 in which thereflection pattern comprises a document type specific pattern.
 6. Thedocument of claim 1 comprising a security document or an identificationdocument.
 7. The document of claim 1 in which presence of the encodedsignal is imperceptible or nearly imperceptible to a human observer ofthe first set of print structures and the second set of printstructures, and in which the first set of print structures and thesecond set of print structures are positioned to obscure a location ofthe second set of print structures on the first surface.
 8. The documentof claim 7 in which the first ink and the second, different ink comprisea metameric pair.
 9. A document comprising: a first surface; a secondsurface, in which the first surface comprises a first set of printstructures and a second set of print structures, and in which the firstset of print structures is provided on the first surface with a firstink, and the second set of print structures is provided on the firstsurface with a second, different ink, and in which the second, differentink comprise a metallic ink, in which the first set of print structuresand the second set of print structures are positioned to obscure alocation of the second set of print structures on the first surface, inwhich the second set of print structures is provided on the firstsurface in a pattern, the pattern yielding an energy signature uponexcitation by a radio spectrum energy source, and in which the radiospectrum energy source emits in the range of 60-75 GHz.
 10. The documentof claim 9 in which the first set of print structures and the second setof print structures are positioned to comprise line-art havingcurvature.
 11. The document of claim 9 in which the first set of printstructures and the second set of print structures are positioned to forman interference image.
 12. The document of claim 9 in which the firstset of print structures and the second set of print structures arepositioned as sets of dots representing a plurality of curving lines.13. The document of claim 9 in which the second set of print structurescomprises metallic dots formed in a reflection pattern on the firstsurface.
 14. The document of claim 9 in which the first set of printstructures are overprinted on or printed adjacent to the second set ofprint structures.
 15. The document of claim 9 in which the second set ofprint structures are provided as a shadow for the first set of printstructures.
 16. The document of claim 9 in which the first set of printstructures and the second set of print structures collective convey anencoded signal discernable from optical scan data representing the firstsurface.
 17. The document of claim 9 in which the first ink and thesecond, different ink comprise a metameric pair.
 18. The document ofclaim 9 in which the first set of print structures or the second set ofprint structures convey an encoded signal which presence of isimperceptible or nearly imperceptible to a human observer thereof, andin which the first set of print structures and the second set of printstructures are positioned as a plurality of curving lines.
 19. Adocument comprising: a first surface; a second surface, in which thefirst surface comprises a first set of print structures and a second setof print structures, in which the first set of print structures and thesecond set of print structures collectively convey an encoded signal, inwhich an encoded signal is detectable from optical scan datarepresenting the first surface, in which the first set of printstructures is provided on the first surface with a first ink and thesecond set of print structures is provided on the first surface with asecond, different ink, and in which the first ink and the second,different ink comprise a metameric pair, and in which the second set ofprint structures is provided on the first surface in a pattern, thepattern yielding an energy signature upon excitation by a radio spectrumenergy source, and in which the radio spectrum energy source emits inthe range of 60-75 GHz.
 20. The document of claim 19 in which the firstset of print structures and the second set of print structures arepositioned to obscure a location of the second set of print structureson the first surface.
 21. The document of claim 19 in which the firstset of print structures and the second set of print structures arepositioned to comprise line-art comprising curvature.
 22. The documentof claim 19 in which the first set of print structures and the secondset of print structures are positioned to form an interference image.23. The document of claim 19 in which the first set of print structuresand the second set of print structures are positioned as a plurality ofcurving lines.
 24. The document of claim 19 in which the first set ofprint structures and the second set of print structures are positionedas sets of dots.
 25. The document of claim 19 in which the second set ofprint structures comprises metallic dots formed in a reflection patternon the first surface.
 26. The document of claim 19 in which the firstset of print structures are overprinted on or printed adjacent to thesecond set of print structures.
 27. The document of claim 19 in whichthe second set of print structures are provided as a shadow for thefirst set of print structures.